Method of making a vapor discharge lamp

ABSTRACT

A metal vapor discharge lamp and method of making the same in which the lamp comprises a partially evacuated translucent ceramic tube containing a charge of metal and a starter gas and hermetically sealed at either end by means of a suitable end cap and electrode assembly which does not have an exhaust tubulation. According to the method of manufacture the evacuation of impurities and residual gases from the lamp and the introduction of the starter gas into the lamp is carried out in the same environment as the sealing of the end cap and electrode assemblies to the ends of the translucent ceramic tube.

United States Patent Inventor Salvatore Cortorilio West New York, NJ.

Appl. No. 23,116

Filed Mar. 1, 1970 Patented Dec. 21, 1971 Assignee Duro-Test CorporationNorth Bergen, NJ.

Original application July 1 1 1967, Ser. No. 652,556, now abandoned.Divided and this application Mar. 1, 1970, Ser. No. 23,116

METHOD OF MAKING A VAPOR DISCHARGE LAMP 5/1963 Lauden et al PrimaryExaminer-John F. Campbell Assistant Examiner-Richard Bernard LazarusAttorney-Darby & Darby ABSTRACT: A metal vapor discharge lamp and methodof making the same in which the lamp comprises a partially evacuatedtranslucent ceramic tube containing a charge of metal and a starter gasand hermetically sealed at either end by means of a suitable end cap andelectrode assembly which does not have an exhaust tubulation. Accordingto the method of manufacture the evacuation of impurities and residualgases from the lamp and the introduction of the starter gas into thelamp is carried out in the same environment as the sealing of the endcap and electrode assemblies to the ends of the translucent ceramictube.

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INVENTOR SALVATORE CORTOR ILLO ATTORNEYS METHOD OF MAKING A VAPORDISCHARGE LAMP This is a division of application Ser. No. 652,556, filedJuly 1 l, 1967, now abandoned.

Because metal vapors and particularly alkali metal vapors are capable ofemitting a large percentage of their total spectral output as continuumradiation, they are recognized as a useful source of radiant emission inelectric discharge lamps, particularly for applications in the visibleand infrared portions of the spectrum. However, in order to achieve highlevels of continuum emission, relatively high metal vapor pressures arerequired. In order to achieve metal vapor pressures of sufficientmagnitude, the metal vapor discharge lamps must be operated at a hightemperatures. Consequently, the various elements of metal vapordischarge lamps must be made of materials which will not be attacked byalkali metal vapors at high temperatures. For example, the translucentenvelope of such a metal vapor discharge lamp might be made of a ceramicmaterial such as polycrystalline alumina or sapphire.

Prior art methods of fabricating electric metal vapor, discharge lampshaving ceramic envelopes generally include the joining of a cylindricaltranslucent ceramic envelope to two formed metal end caps to whichsuitable electrodes have been attached. One of the end caps is providedwith a small hollow tube, known as an exhaust tube, which permits theassembled lamp to be evacuated and the necessary metals and startergases to be introduced. Because of the high-operating temperatures ofthe finished lamp, both the end caps and the exhaust tubing must be madeof refractory materials. In addition, these materials must haveapproximately the same coefficient of thermal expansion as the ceramicenvelope. Further, the ceramic envelope, the electrodes, the end caps,and the exhaust tubing must be made of materials which are able towithstand the corrosive effect of alkali metal vapors used in the lampat the requisite high-operating temperatures.

In the prior art method of manufacturing these types of lamp, the endand electrode assemblies are first hermetically sealed at both ends ofthe translucent ceramic tube and the sealed lamp assembly is connectedto an exhaust system by means of the abovementioned exhaust tube.Impurities and residual gases are then evacuated from the lamp throughthe exhaust tube and the required metals and starter gases areintroduced. The exhaust tube is then cold welded or pinched off at apoint along its length so as to finally hermetically seal the lamp anddetach it from the exhaust system.

One problem occurring in metal vapor discharge lamps constructedaccording to the methods of the prior art is that during the operationof the lamp alkali metal vapors tend to condense in the cavity of thetip of the exhaust tubing remaining in the lamp envelope because of thelarge temperature difference which exists between the end cap of thelamp and this extreme tip of the pinched ofi' exhaust tube.

A second problem of the prior art methods of manufacture arises from thedifficulty of removing all traces of the metallic emission material ofthe electrodes from the exhaust tube prior to the pinching offoperation. Any traces of metal or metal condensate will destroy therequired cleanliness and surface structure of the inner wall of theexhaust tube and thus prevent a proper cold weld.

A third problem of the prior art methods of manufacture is the generaldifficulty of pinching off of cold welding the refractory material ofthe exhaust tubing without causing mechanical damage. For example,refractory metals such as columbium and tantalum have a fibrousstructure which demands great care, control instrumentation andequipment in order to successfully achieve a pinch off.

The present invention relates to electric discharge lamps of the typewherein the source of radiant emission comprises a combination of metalvapors and inert starter gases. More particularly, this inventionrelates to metal vapor electric discharge lamps having translucentceramic envelopessuch as, for example, polycrystalline alumina orsapphire envelopes, which are fabricated without the use of the exhausttubing required by conventional lamps. The invention further relates toa method of making metal vapor discharge lamps in which the evacuationof impurities and residual gases and the introduction of the necessarymetals and starter gases are accomplished without the use of specialexhaust tubing.

. It is therefore an object of this invention to provide an improvedmetal vapor discharge lamp and method of manufacture which obviate theproblems of the prior art devices and methods.

More particularly it is an object of this invention to provide animproved metal vapor discharge lamp having no vestigial exhaust tubingtip.

It is also an object of this invention to provide an improved method ofmanufacturing metal vapor discharge lamps which does not require the useof exhaust tubing.

It is a further object of this invention to provide a method ofmanufacturing metal vapor discharge lamps wherein the evacuation ofimpurities and residual gases from the lamp and the introduction of therequired metals and starter gases into the lamp are integral with thesealing of the end caps to the translucent ceramic envelope.

According to the above and other objects, this invention provides ametal vapor discharge lamp comprising a translucent ceramic envelopehaving an end cap and electrode assembly sealed at either end thereofand containing suitable metal emission materials and inert startergases. As hereinafter described the ends of the lamp do not have theusual exhaust tubes.

The method of manufacturing the discharge lamp of the present inventionincludes disposing the translucent ceramic tube and a first end capassembly within an evacuated gastight chamber, heating the ceramic tubeand end cap so as to first drive of? impurities and residual gases andthen bond the tube and one end cap in a gastight seal, inserting acharge of metal into the ceramic tube to provide a source of radiantemission in operation, positioning a second end cap at the open end ofthe tube, heating the ceramic tube and second end cap so as to againdrive off impurities and residual gases, introducing a starter gas intothe ceramic tube, further heating the ceramic tube and second end cap soas to bond the tube and end cap in a gastight seal, and removingtheassembled lamp from the gastight chamber.

Other objects and advantages of the present invention will be moreclearly understood from the following description and accompanyingdrawings which set forth the principle of the invention and, by way ofexample, the preferred mode which has been contemplated of applying thatprinciple.

FIG. 1 is a sectional view of the metal vapor discharge lamp of thepresent invention;

FIG. 2 is a cross-sectional view taken along the line 2-2 of the lampshown in FIG. 1;

FIG. 3 is a sectional view of a portion of the apparatus used in themethod of manufacture of the metal vapor discharge lamps of the presentinvention showing a lamp mounted therein;

FIG. 4 is a sectional view of a modified form of the apparatus used inthe method of manufacturing discharge lamps according to the presentinvention, also showing a lamp mounted therein;

FIG. 5 is a detailed sectional view of an end car and electrode assemblyfor the discharge lamp of the present invention, and

FIG. 6 is a detailed sectional view of a modified form of an end cap andelectrode assembly for the discharge lamp of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 show a metal vapordischarge lamp including a transparent or translucent envelope, 1, whichmay, for example, be in the form of a tube, as shown. Envelope 1 may bemade of any material which is transparent or translucent over asubstantial portion of the spectrum of the lamps emitted light and whichis able to withstand the effects of the alkali metal vapors at thehigh-operating temperatures encountered.

For example, translucent envelope 1 may be made of a ceramic materialsuch as polycrystalline alumina or sapphire.

An end cap 4 is secured to each end of the translucent envelope 1. Endcaps 4 maybe made of any refractory material having approximately thesame coefficient of thermal expansion as the material of translucentenvelope 1 and which is able to withstand attack by alkali metal vaporsat high temperatures. For example, end caps 4 may be made of refractorymetal such as columbium or tantalum.

Secured to each end cap 4 is an electrode 2 which may be made, forexample, of tungsten. As shown in greater detail in FIG. 5, electrode 2may comprise a coil 20 or coils of tungsten wound on a tungsten rod 2b.If desired a suitable electron emission material such as, for example,Thorium oxide suspended in N-propanol may be applied to the innersurface of coil 2a. The rod 2b of electrode 2 is joined to end cap 4 inany suitable manner such as, for example, by brazing with titaniumbrazing material 3.

End caps 4 are preferably secured to the ends of translucent tube 1 by aquantity of material of frit composition 5. The frit composition 5 maybe for example, one or more glasses such as silicon dioxide suspended ina suitable suspending agent or vehicle such as, for example, butylacetate. The frit composition 5 is applied to the inner surfaces of endcap 4 which is then placed in position at one end of translucent tube 1.Heat is then applied to drive off impurities and residual gases such as,for example, water vapor and/or traces of this frit-suspending agent.Further heating causes the glass frit to fuse and flow so as to form ahermetic seal between translucent tube 1 and end cap 4 as will beexplained below in greater detail.

The assembled metal vapor discharge lamp of FIGS. 1 and 2 contains acharge of metal which serves as a source of metal vapor for the lamp inoperation. For example, the lamp of FIGS. 1 and 2 contains a quantity ofsodium 7 which provides the principal source of radiant emission and aquantity of mercury 7 which acts as a buffer. In addition, the lamp ofFIGS. 1 and 2 may contain a suitable starter gas such as xenon, forexample. Although mercury and sodium are typical metals and xenon is atypical starter gas for use in the present metal vapor discharge lamp,it will be recognized by those skilled in the art that other metals andstarter gases might be employed.

FIG. 3 illustrates apparatus which may be employed to carry out themethod of manufacturing metal vapor discharge lamps of the presentinvention. A bell jar base plate 8 together with a suitable bell jar 20form a gastight chamber in which the fabrication of the discharge lampis carried out. In the apparatus of FIG. 3 base plate 8 also acts as aheat sink during the fabrication of the lamp. Base plate 8 is thereforemade of a suitable material having high-thermal conductivity such as,for example, aluminum. Heat is carried away from plate 8 by means of asuitable coolant such as, for example, water circulating through coolingcoils 9 which are disposed beneath base plate 8 in a heat conductiverelationship.

Secured to base plate 8, for example, by screw 13b or any otherfastener, and projecting upward therefrom is a receptacle 13 forreceiving and holding one end of the metal vapor discharge lamp duringthe fabrication process. Receptacle 13 is made of a material ofhigh-thermal conductivity such as, for example, brass, and is in thermalcommunication with base plate 8 with the result that receptacle 9 actsas a heat sink which draws heat away from the lower end of the lampduring the fabrication process. Base plate 8 and receptacle 13 each havea central passageway 9a and 130, formed by a bore or tube, connectingthe interior of the gastight bell jar chamber to a suitable exhaustsystem, not shown, through which the bell jar can be evacuated. i

Located within the bell jar enclosure is a heat source for supplying thenecessary heat to carry out the various steps of the fabrication processas will be explained below in greater detail. In the preferred form ofthe apparatus shown in FIG. 3,

the heat source comprises a cylindrical metal susceptor 10, preferablymade of molybdenum or tungsten. Cylindrical susceptor is positionedcoaxially with the lamp being fabricated and surrounds the upper end capof the lamp when the lower end of the lamp is inposition in receptaclel3. As will be appreciated by those skilled in the art, metal susceptor10 is capable of being heated by eddy currents induced in the susceptorby a suitable induction coil, not shown, which may be located outsidethe bell jar. The heat thus generated is transmitted by radiation fromsusceptor 10 to end cap 4 and ceramic envelope 1 of the lamp to befabricated. Susce'ptor 10 may be supported in position by any suitablemeans such as, for example, cylindrical ceramic support member 11 whichrests on the upper surface of receptacle 13 as shown in FIG. 3. Inaddition, there may optionally be provided a tube of polycrystallinealumina 12 concentrically surrounding the lamp to be fabricated andserving as an evaporation protecting shield.

According to the present invention, the metal vapor discharge lamps arefabricated in the following manner. First, an end cap and electrodeassembly such as that shown in FIG. 5 is prepared for assembly byspreading a glass frit composition 5 on the inner surfaces of the endcap 4. The translucent ceramic tube is then placed in position inreceptacle 13 as shown in FIG. 3. If desired, one or more asbestos shims14 may be inserted so as to hold translucent tube 1 in position inreceptacle 13. The end cap and electrode assembly which has beenprepared with the glass frit composition is then placed in position atthe upper end of translucent tube I. Susceptor 10, support member 11,and evaporation shield 12 are arranged as shown in FIG. 3. The bell jaris then lowered over the entire assembly and sealed to base plate 8 soas to form a gastight chamber which is then evacuated by means of asuitable exhaust system through the passage 13a in receptacle l3. Aninduction heater coil is placed over the bell jar and positionedconcentrically with susceptor 10 which, in turn, surrounds thecomponents to be sealed. Alternating current is then applied to theinduction coil thus heating susceptor 10. As the power applied to theinduction coil is gradually increased, the temperature of susceptor l0gradually increases thus causing increasing amounts of heat to beapplied to the components of the lamp to be fabricated. Because theheating process is carried out in a vacuum, impurities and residualgases trapped in the lamp components are driven off at intermediatetemperatures of about 600 C. to 1,200 C. The temperature is graduallyfurther increased to approximately l,600 C. at which temperature theglass frit fuses and flows to form a her metic seal between metal endcap 4 and translucent ceramic tube 1. The sealed components are thenallowed to cool gradually to room temperature. If desired, a quantity ofinert gas may be introduced into the chamber through passage 13a oranother passage shown) to speed up the cooling process. For example,argon gas at mm. pressure might be introduced into the chamber for thispurpose.

When the sealed components have reached room temperature, the bell jaris removed and the partially assembled lamp is inverted so that themetal end cap 4 rests in receptacle l3 and the open end of translucentceramic tube 1 faces upward. At this point a suitable charge of metalmay be introduced into the open end of translucent ceramic tube 1 toprovide a source of metal vapor for the lamp in operation. For example,in the preferred form of the invention, small quantities of sodium 6 andmercury 7 are introduced into the partially assembled lamp. lt will beappreciated by those skilled in the art that the handling of the sodiummetal 6 should preferably be carried out in an inert protectiveatmosphere to prevent the undesired reaction of the sodium with oxygenand water vapor present in an air atmosphere.

The second end cap and electrode assembly is prepared with the glassfrit composition and placed in position over the open end of translucentceramic tube 1. The bell jar and induction coil are then replaced, thechamber is evacuated, and power is applied to the induction coil so asto heat susceptor 10. Once again the temperature of the components to besealed is gradually increased to a temperature sufficient to drive offimpurities and residual gases, but not sufficient to cause the glassfrit to fuse and flow. As explained above, a temperature of about 600 C.to l,200 C. is sufficient to drive off impurities and residual gasessuch as, for example, water vapor and/or traces ofthe frit suspendingagent.

After the impurities and residual gases have been driven off, i

a starter gas may be introduced into the chamber and thus into thepartially assembled lamp through the as yet unsealed joint between theend cap 4 and the translucent ceramic tube 1. For example, a quantity ofinert gas such as argon or xenon at a pressure of approximately 30 mm.of mercury may be introduced for this purpose. Increased power is thenapplied to the induction coil so as to heat the lamp components to atemperature sufficient to cause the glass frit to fuse and flow and forma hermetic seal between the metal end cap 4 and the translucent tube 1.As described above, the glass frit employed in this illustrative examplefuses and flows at approximately l,600 C. After the hermetic seal hasbeen affected, the assembled lamp is allowed to cool to roomtemperature. Inert gas may be used to speed the cooling process asexplained above.

During the heating and sealing of the second end cap 4 to thetranslucent ceramic tube 1, the first end cap 4 and hermetic seal aremaintained at a reduced temperature by means of the heat sink formed byreceptacle 13, base plate 8, and cooling coils 9. In this manner thefirst hermetic seal is kept intact during the formation of the secondseal. The heat sink also helps to keep the sodium and mercury particles6 and 7 respectively from being vaporized by the heat of the sealingprocess.

Proper control of the heating and cooling cycles is important in orderto obtain consistently good seals. Generally, the heating cycle shouldbe sufficiently slow to avoid cracking the components, to permitimpurities and residual gas to be completely exhausted, and to permitthe glass frit to fully flow to form a hermetic seal. The maximumtemperature reached should not be so high as to crack the components,and likewise, the cooling cycle should be sufficiently slow to avoidcracking. The precise relationship between time and temperature dependsupon the particular materials used, and different optimum timetemperature relationships can probably be established for each differentcombination of materials. For purposes of illustration, satisfactoryresults have been obtained for the combination of a polycrystallinealumina tube, columbium end cap, and Coming No. l73l glass fritcomposition by heating the components to be sealed from room temperatureto approximately 1,600 C. at an approximately uniform rate over a periodof approximately four minutes and then cooling in an atmosphere of 100mm. of argon for approximately minutes. It will be recognized, however,that the present invention is not limited to any particular heating andcooling cycle, but that it embraces any heating and cooling cycle whichdoes not crack or otherwise damage the components and which allows thefrit composition binders, impurities, and residual gases to be drivenoff before the frit is caused to fuse, flow and form a good, gastighthermetic seal.

FIG. 4 shows a modified form of apparatus for carrying out the presentmethod of manufacturing metal vapor discharge tubes. The apparatus ofFIG. 4 permits the introduction of a highly pure charge of metal intothe lamp envelope. The apparatus of FIG. 4 includes an evacuable housingwith lower and upper sections 17 and 18 separated by a wall 19 formingchambers 17a and 18a. A vacuum gate valve 26 is located on the uppersurface of wall 26 and is operable by a control handle 26a which extendsoutside of the housing through a suitable vacuum seal. The portion ofthe housing 18 forming upper chamber 180 is preferably made of amaterial such as columbium or stainless steel which are resistant toattack by alkali metal vapors. An O-ring seal block 20 is secured, as bythreaded engagement, to the top of of upper housing section 18. A pairof O-rings 23 form a gastight circumferential seal around a piece oftubing 22 which extends through O-ring seal block 20 into upper chamber18a. The tube 22 is slidable up and down within the O-rings. A T-portion29 of tube 22 holds a capsule 24 containing the quantity of predistilledmetal to be introduced into the lamp during the fabrication process,Tube 22 extends above T-portion 29 so as to permit a steel slug 30 to beraised by a magnetic coil 31 as shown. When released by magnetic coil31, steel slug 30 impacts and breaks capsule 24 causing the charge ofmetal to flow down through tube 22 into the waiting lamp envelope aswill be explained below in greater detail. Tube 22 may be made of glassor quartz or other material depending on the type of metal charge to behandled.

The lower housing portion 17 includes a quartz cylinder which rests onbase plate 8 and forms a gastight seal therewith. The quartz cylinder isjoined to upper housing portion 18 by a graded quartz to Kovar" seal 15.Gate valve 26 controls the opening in wall 19 between upper chamber 18aand lower chamber 17a.

Using the apparatus of FIG. 4, the method of manufacturing metal vapordischarge lamps is as follows. First, an end cap and electrode assemblyof the type shown in FIG. 5 is prepared with a suitable glass fritcomposition. The translucent ceramic tube 1 is placed in position inreceptacle 13, the fritted end cap 4 is placed in position on the upperend of tube 1 and the bell jar assembly 17-18 18 is placed in positionwith valve 26 closed. Lower chamber 17 is evacuated, and the lampcomponents to be sealed are gradually heated by susceptor 10 to driveoff impurities and residual gases and finally to cause the frit to fuse,flow, and form a gastight seal between end cap 4 and tube 1. The lamp isthen cooled to room temperature and inverted so that the sealed endrests in receptacle 13. A glass frit composition is then applied to theinner surfaces of the modified form of end cap and electrode assemblyshown in FIG. 6. In the modified assembly of FIG. 6, tungsten electrode,2 is brazed at an angle to columbium or tantalum end cap 4 with titaniumbraze 3. An opening 27 is formed at or near the center of end cap 4.Glass frit composition 28 is applied around the edges of opening 27 asshown.

After the inner surfaces of end cap 4 of FIG. 6 have been prepared withthe glass frit composition 5, the end cap and electrode assembly isplaced in position on the upper, open end of translucent ceramic tube 1.The bell jar assembly of FIG. 4 is then placed in position with gate 26open so that both lower chamber 17 and upper chamber 18 may beevacuated. Heat is then applied by means of susceptor 10 in order todrive off impurities and residual gases. This step is preferably carriedoutprior to the introduction of the charge of metal in order to avoidpossible reaction between the metal and the impurities.

The tip 34 of tube 22 is then moved downward to a position immediatelyabove the opening 27 in end cap 4, and steel slug 30 is raised and thenreleased by magnetic coil 31 so as to break capsule 24 and allow thecharge of metal to flow down through tubing 19 into the lamp via opening27. If desired, external heat may be applied to tube 22 to induce thecharge of metal to flow down into the lamp.

After the charge metalhas been introduced into the lamp, tube 22 iswithdrawn upward, gate 26 is closed, and an inert starter gas may beintroduced into lower chamber 17. Further heat is then applied to causefrit 28 to fuse and flow to seal opening 27 in end cap 4. Frit 5 fusesand flows to form a hermetic seal between end cap 4 and translucentceramic tube 1. As described above in connection with FIG. 3. the heatsink" formed by receptacle 13 and base plate 8 serves also to preventthe metal charge from evaporating during the sealing of the second endcap to the upper end of ceramic tube 1. After the seal has been formed,the assembled lamp is gradually cooled to room temperature with theoptional aid of an inert gas at approximately I00 mm. of pressure.

Although the present invention has been illustrated by reference to apreferred embodiment, it will be apparent to those skilled in the artthat certain modifications may be made without departing from theprinciples of the invention. For example, the principles of the presentinvention embrace a method of manufacturing metal vapor discharge lampswherein the heat required-for sealing the metal end caps to thetranslucent ceramic tube is generated by including eddy currents in theend caps themselves, no separate susceptor being required.

Further, the principles of the present invention embrace a method ofmanufacturing metal vapor discharge tubes wherein both end caps aresimultaneously sealed to the ends of the translucent ceramic tube.

It will be apparent to those skilled in the art that other modificationsand adaptations of the present invention may be made without departingfrom the spirit and scope of the invention as set forth withparticularity in the appended claims.

What is claimed is:

l. The method of making a metal vapor discharge lamp comprising thesteps of disposing a translucent tubular envelope within an evacuatedgastight chamber;

securing a first end cap and electrode assembly to one end of saidenvelope to form a gastight seal;

inserting a charge of metal into said envelope through an opening in asecond end cap and electrode assembly to provide a source of metal vaporfor the operation of said lamp;

introducing a starter gas into said envelope; thereafter heating tosecure said second end cap and electrode assembly to the other end ofsaid envelope and to form said seal opening and thereby form a gastightseal; and

removing the assembled lamp from said gastight chamber.

2. The method of claim 1, further comprising the step of heating theenvelope to outgas it.

3. The method of claim 2, wherein said outgassing step is carried outprior to securing the first end cap to the envelope.

4. The method of claims 2, wherein the outgassing step is also carriedout prior to securing the second end cap to the envelope.

5. The method of claim 1, wherein the end caps and elec trode assembliesare sealed to the envelope by providing frit between the end caps andthe ends of the envelopes and further comprising the step of heating thefrit to cause it to flow to form the seal.

6. The method of claim 1, wherein the first end cap is sealed to theenvelope by providing frit between the first end cap and one end of theenvelope and the heating of the envelope and the first end cap iscarried out to a first temperature to drive off impurities and outgasthe envelope, and then the heating of the envelope and first end cap iscarried out to a second and higher temperature to cause the frit to flowand form a gastight seal.

7. The method of claim 6, wherein the second end cap is sealed to theenvelope by providing frit between the second end cap and the other endof the envelope and the heating is carried out to a first temperature todrive ofi' impurities and outgas the envelope, and then the heating ofthe envelope and the second end cap is carried out to a second andhigher temperature to cause the frit to flow and form a gastight seal.

8. The of claim 6, wherein said first temperature is in the rangebetween about 600 C. and l200 C.

9. The method of claim 1, further comprising the step of holding thefirst end cap and electrode assembly in heat-conductive relationshipwith a heat sink while the second end cap is being secured to theenvelope.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 2Dated December 21, 1971 Inventor(s) SALVATORE COR'I'ORILLO ItViscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col. 1, line 36, change "lamp" to lamps Col. l, line 36, after "end"insert cap Col. 2, line 60, delete "car" and insert cap Col. 4, line 51,after "passage" insert --(not Col. 5, line 17, after "been" delete"affected" and insert effected Col. 6, line 24, delete "l8" secondoccurrence) Col. 6, line 57, insert "of" before "metal" Col. 7, line 26,delete "form said" Col. 7, line 27, insert said before "opening" Col. 8,line 2, delete "claims" and insert claim -Col. 8, line 25, insert"method" after "The" I Page 1 of the Patent, the filing date of the apolication should be March 10, 1970, not March 1, 1970.'

Signed and sealed this 29th day of Ootober 1971,.

(SEAL) Attest MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting OfficerCommissioner of Patents FORMPO-WSO (10-69) USCOMM-DC wan-ps9 U 5.GOVERNMENT PRINTIFG OFFICE K1559 355'334.

1. The method of making a metal vapor discharge lamp comprising thesteps of disposing a translucent tubular envelope within an evacuatedgastight chamber; securing a first end cap and electrode assembly to oneend of said envelope to form a gastight seal; inserting a charge ofmetal into said envelope through an opening in a second end cap andelectrode assembly to provide a source of metal vapor for the operationof said lamp; introducing a starter gas into said envelope; thereafterheating to secure said second end cap and electrode assembly to theother end of said envelope and to form said seal opening and therebyform a gastight seal; and removing the assembled lamp from said gastightchamber.
 2. The method of claim 1, further comprising the step ofheating the envelope to outgas it.
 3. The method of claim 2, whereinsaid outgassing step is carried out prior to securing the first end capto the envelope.
 4. The method of claims 2, wherein the outgassing stepis also carried out prior to securing the second end cap to theenvelope.
 5. The method of claim 1, wherein the end caps and electrodeassemblies are sealed to the envelope by providing frit between the endcaps and the ends of the envelopes and further comprising the step ofheating the frit to cause it to flow to form the seal.
 6. The method ofclaim 1, wherein the first end cap is sealed to the envelope byproviding frit between the first end cap and one end of the envelope andthe heating of the envelope and the first end cap is carried out to afirst temperature to drive off impurities and outgas the envelope, andthen the heating of the envelope and first end cap is carried out to asecond and higher temperature to cause the frit to flow and form agastight seal.
 7. The method of claim 6, wherein the second end cap issealed to the envelope by providing frit between the second end cap andthe other end of the envelope and the heating is carried out to a firsttemperature to drive off impurities and outgas the envelope, and thenthe heating of the envelope and the second end cap is carried out to asecond and higher temperature to cause the frit to flow and form agastight seal.
 8. The of claim 6, wherein said first temperature is inthe range between about 600* C. and 1200* C.
 9. The method of claim 1,further comprising the step of holding the first end cap and electrodeassembly in heat-conductive relationship with a heat sink while thesecond end cap is being secured to the envelope.